CUOMO: Good morning. Welcome to NEW DAY. It is Friday, June 13th, Friday the 13th, 6:00 on the east. Kate is on vacation. Very nice to have Brianna Keilar here with us this morning.

KEILAR: Great to be here.

CUOMO: It is nice to have you. Overnight, we have breaking news for you, Sergeant Bowe Bergdahl as we said back on U.S. soil after five years in Taliban captivity. The 28-year-old arriving over night at Brook Army Medical Center in San Antonio, Texas. Bergdahl's return is, of course, overshadowed by questions about his disappearance and controversy over the Taliban prisoner swap that freed him.

CNN's Martin Savidge joins us from San Antonio with the latest developments. Good morning, Martin.

MARTIN SAVIDGE, CNN CORRESPONDENT: Good morning, Chris. Yes, U.S. military officials tell me that the most critical part of Sergeant Bowe Bergdahl's return to freedom begins right now and very important to that will be the reunion with his family.

(BEGIN VIDEOTAPE)

SAVIDGE (voice-over): After five years in Taliban captivity, U.S. Army Sergeant Bowe Bergdahl is back on American soil. Touching down overnight Bergdahl arrived at Lackland Air Force Base in San Antonio and was transported to a military medical facility with a room prepped for his arrival and a support team standing by along with his family.

REAR ADMIRAL JOHN KIRBY, PENTAGON SPOKESMAN: He just came out of five years of captivity. We're going to get a chance to find out what was in his head there that day when he was taken captive.

SAVIDGE: "The Daily Beast" obtained letters purportedly written by Sergeant Bergdahl to his family while he was in captivity. They may give a glimpse into his disappearance from his base at night in 2009, writing, leadership was lacking, if not non-existent. The conditions were bad and looked to be getting worse for the man that were actually the ones risking their lives from attack.

The two letters are dated 2012 and 2013. Penned in two very different writing styles. One in cursive. The other in block print. The Bergdahl family purportedly confirmed the authenticity of the letters revealed by sources in contact with the Taliban. Held hostage in Iraq for nearly a year, American Roy Hallums can relate.

ROY HALLUMS, AMERICAN HOSTAGE IN IRAQ FOR 10 MONTHS: When I did mine they set a piece of paper in front of me and gave me a pen and one person sat on each side of me and told me exactly what words to write and they wanted me to print it and not write it in script because they couldn't read English in script.

SAVIDGE: At times, Bergdahl's thoughts seemed to wander, touching on mathematics, God, and the universe. Several portions of the letter blocked out, it's unclear by whom. Words in letters oddly misspelled. In 2013 he wrote, if this letter makes it to the USA tell those involved in the investigation that there are more sides to the cittuwation (ph)."

(END VIDEOTAPE)

SAVIDGE: The reunion with his family, everybody wants to know when is that going to happen. The military says there is no specific timeline. It will take place inside the hospital where Bowe Bergdahl currently is. It will take place in a room and it will be very carefully handled, first meeting only expected to last a few minutes -- Brianna.

KEILAR: Martin Savidge for us in Texas. Thank you.

Now to Iraq where bloody chaos is taking over. Radical Islamists now closing in on the capital. Days after they seized Mosul, the country's second largest city, now they're moving south nearing Baqubah and getting perilously close to Baghdad.

CNN is all over this story and we're going to begin with senior international correspondent, Arwa Damon. She is tracking developments from Iraq -- Arwa.

ARWA DAMON, CNN SENIOR INTERNATIONAL CORRESPONDENT: Good morning and the situation for Iraq could not be in the words of one Iraqi politician, more catastrophic.

(BEGIN VIDEOTAPE)

DAMON (voice-over): Leaving no doubt about their reach video claiming to show the radical Islamist terrorist group, ISIS, arriving to cheers in Syria with an Iraqi army military Humvee. ISIS gaining control, not just over land but armored vehicles, weapons, and ammunition, abandoned by the Iraqi forces as they fled Mosul, Iraq's second largest city.

Parts of Baiji, an oil refining town, an area surrounding the oil city of Kirkuk also seized by ISIS, prompting Kurdish forces to send in their troops after the Iraqi military fled there as well. And in this video from Saddam Hussein's hometown of Tikrit purporting to show fighters parading hundreds of captured Iraqi security forces.

HOSHYAR ZEBANI, IRAQI FOREIGN MINISTER: They have melted down unfortunately. Two army divisions in the city and their commanders escape to the north, and really the government needs to take serious action.

DAMON: With ISIS threatening that Baghdad is next, U.S. contractors were evacuated from an Iraqi military base and chartered out of the country. Still, some U.S. commanders remain optimistic about the Iraqi security forces they left behind.

ADMIRAL WILLIAM FALLOW, FORMER COMMANDER, U.S. CENTRAL COMMAND: They've got a lot of equipment and they have some of their forces are pretty well strained, I believe, by our folks and NATO, allies before we left. So I think they have the capabilities to do this.

DAMON: Nearly three years after American boots left Iraqi soil, a terrorist group more powerful than al Qaeda is gaining greater control.

(END VIDEOTAPE)

DAMON: Brianna, one of the main reasons that ISIS is able to gain territory so quickly is that other Sunni insurgent groups have also emerged in the fight against the predominantly Shia government of Nuri al-Maliki. The situation in Iraq is not going to come under control by sheer of military might along. There has to be true political reconciliation.

BALDWIN: Arwa Damon for us in Erbil, thank you. Now the Iraqi government is asking the U.S. for help. President Obama says he's not ruling anything out. Let's bring in our senior White House correspondent, Jim Acosta. Not ruling anything out, what does that mean, Jim?

JIM ACOSTA, CNN WHITE HOUSE CORRESPONDENT: Brianna, it does mean that the U.S. is now considering air strikes. The president met with his national security team to talk about options to contain the growing crisis in Iraq. Here are some of the options that the White House is talking about at this point.

The president is considering drone or air strikes to contain the movements made by ISIS in Iraq. He's also talking about ramping up military aid to Iraqi fighters. At the same time, they are putting new humanitarian assistance in the pipeline. But keep in mind, despite the president said that he is not ruling anything out, there will be no boots on the ground.

Administration officials saying no boots on the ground. That is not being considered. Keep in mind, at the same time, with the Sunni- backed fighters making these advances in Iraq and even some U.S. contractors being evacuated from the country time is considered of the essence over here at the White House. That is why senior administration officials are indicating a strike could come as early as this weekend. Meanwhile, we should also point out White House officials are deeply frustrated with Iraqi Prime Minister Nuri Al-Maliki. They believe he has failed to unite the warring factions in Iraq leading to this crisis. That is why any U.S. action, White House officials are cautioning would be short lived and keep in mind for a president who pledged back in 2008 to end the war in Iraq and then did so in 2011, there is great political risk for this president -- Chris.

CUOMO: All right, Jim, speaking of failure there is plenty of it to go around in this situation. So let's get into it. For more on who ISIS is, how dangerous they are, what's going to happen next, let's bring in Bobby Ghosh. He is "Time" magazine's world editor. Bobby, it's good to have you back here.

One quick editorial point before we get into the particulars here, no boots on the ground. We need political reconciliation to make this stop. That sounds like almost magic talking about this point now. From what we understand about the situation, is there any way that air strikes would be enough? Is there any chance at any kind of political reconciliation right now?

BOBBY GHOSH, WORLD EDITOR, "TIME" MAGAZINE: Not at the moment. You don't know who to strike. Air strikes involve intelligence. Intelligence means you have to trust the people giving it information. We talk about Iraqi government whose own military doesn't trust it. They walked away. They walked away because they didn't feel they had a stake in the future of their country.

The Kurds don't trust their government. Many Sunnis don't trust their government. How can the United States trust any intelligence that comes out of the government of Nuri Al-Maliki? So air strikes, boots on the ground, these things are simply not part of the equation right now.

CUOMO: All right, so now we're dealing with really a three-tiered problem. Even to keep it simple. We're focusing on ISIS, OK. ISIS, is the militant group, the acronym ISIS is basically Islamic State in Iraq and Syria. You told us already they are different because they are not about chaos. They are about land grab and control. Explain.

GHOSH: Well, most terrorist groups that we're familiar with in modern times, all they want to do is mayhem. They want to kill a lot of people. They talk about going to paradise. They talk about the perfect Islamic state. But this is a group that is actually seizing territory, holding on to it, appointing governors, appointing local administration.

They seem like they want to rule. They want a nation on this earth, not the one in paradise and that makes them very different. That's a different level of ambition than we've seen from let's say, Osama Bin Laden or people from his group.

CUOMO: And you see it in their plan. We are impressed by the speed. They're over taking the country. Almost no resistance, but they're being smart. Mosul, why do they want Mosul? It's the second biggest city, but huge cultural cache to it, historical importance. Basically the metaphor is, if I control this I control what matters. True?

GHOSH: Mosul is an ancient city. It's a very important business center. It has been for hundreds of years. It is the home of many of Iraq's most famous military commanders. Mosul prides itself as a city that gave Iraq its greatest military commander. So there's a big political and propaganda message being sent when they take Mosul.

CUOMO: They just rolled through.

GHOSH: They came down this route faster than the United States and its coalition went up in 2003. That speed is incredible. They travel very light, very fast and they are traveling, let's not forget, a lot of this is Sunni part of the country. So they are traveling in territory if not friendly is certainly not hostile towards them and their interest.

CUOMO: Now we believe they're headed toward Baghdad. They are getting very little resistance. Kirkuk is also important because when they took that city it triggered second layer of problem now if it's not just that they have to deal with ISIS in Iraq, but now the Kurds who believe Kirkuk should be theirs, so now you have this tribal movement. They come down.

Now they're controlling Kirkuk. So ISIS is gone, but you have a new set of not bad guys, but people who are against the Iraqi government in control. And as they move toward Baghdad you have the Sunni-Shia dynamic coming into play where the Shia military types. You know, the militias are being asked to come in to defend the city, three layers of trouble? Accurate?

GHOSH: Absolutely. With the Kirkuk, the Kurds, these are friends of ours. They fought alongside the American military against Saddam Hussein. They are fabled fighters. Known for their ferocity. The name Peshmerga is known for death. They are not going to easily gave it back to the government in Baghdad.

They wanted Kirkuk for a very, very long time. Kirkuk is an oil city. Giant -- it sits on a super lake of oil. At strategic importance, economic importance and for Baghdad to get back is going to require -- state is going to shift of a level that they don't currently have.

CUOMO: So what we start to see is this man at the center of ISIS and as we touched the center of the nose, here is a different picture of the guy. When you look at the precision, the speed, the acquiring of assets and cash because he's emptying the banks and the momentum he's getting among the people, how do we see this man and what his future is?

GHOSH: He is now probably the most successful modern terrorist because he holds all of that territory. That's the country the size of Jordan. There are only three or four pictures of this guy and that's part of his power that nobody really knows him. There are no videos of him. They wanted to audiotapes out there that we think may be --

CUOMO: Better known for his ambition. Everything that you see in dark now on your screen he believes should be under their control of one true Islamic state and it almost includes Israel.

GHOSH: Nobody can say these guys haven't told us what they want. It's very clear what they want. They want all of this territory and this includes, as you say, Israel, all of Iraq's oil, bordering on some incredibly, you know, ally here, arrival there --

CUOMO: You've mentioned to me before we came on, there's word that revolutionary guard from Iran are on the ground in Iraq to help the state, but to the Iraqis that's just more destabilizing because of the history with Iran.

GHOSH: There were reports of that yesterday. If it was true it would be like throwing a grenade into an armory because Iraq and Iran fought eight-year bloody war. Half a million Iraqis died. Even Iraqi Shiites are not particularly fond of them. And so the idea that Iranian boots are on the ground in Iraq, even if to protect Baghdad, that would be very humiliating to a lot of Iraqis.

CUOMO: Remember this, right now we're hearing from U.S. authorities, no boots on the ground. We're going to do some drone strikes, help with the military. It doesn't even end in Iraq, even if the drone strikes were effective and what's the real chance of that and no boots on the ground.

It all emanates from Syria so you would have to be involved there as well. It's very complicated, very layered and moving very quickly. Bobby Ghosh, thank you very much. I'm sure to have you back to help me understand this as we move forward.

GHOSH: Happy to do it.

CUOMO: Brianna.

KEILAR: Thanks, Chris. Next up on NEW DAY, new video of Bowe Bergdahl back in the U.S. as just published letters cast new light on why he may have disappeared. We're talking to the reporter who obtained those letters.

And New Jersey Governor Chris Christie is noticeably slimmer and also busting a move on late night TV. Talking trash as well, not about Hillary Clinton's politics, but her dancing skills.

(COMMERCIAL BREAK)

CUOMO: We have new video just in to CNN of Sergeant Bowe Bergdahl as he is back on U.S. soil landing just hours ago. He is now at Brook Army Medical Center in Texas. That's where he will be doing the next stage of recovery from five years in Taliban captivity.

Now, of course, the big question isn't where he is, it's why he left his post in the first place?

And we may be getting some information that pushes us toward an answer there. Newly published letters written by Bergdahl, we believe.

Joining us this morning is Kimberly Dozier. She's contributing as the writer of "The Daily Beast" article about this. She obtained the letters.

Kim, it's good to see you.

This is important here because this question is plaguing the analysis of the deal to bring Bergdahl home.

Let's start with the letters. The authenticity is the obvious question. What can you tell us about authorship and whether they were under duress?

KIMBERLY DOZIER, CONTRIBUTING WRITER, THE DAILY BEAST: There are two letter 'one from 2012 and one from 2013. I have to say the first time I saw them I thought, this is a joke. These can't really have been written by Bowe Bergdahl himself. Then I showed them to U.S. officials, western I was officials who had been part of this whole process to try to get him back. They said, no, those are the real things that the Red Cross delivered to Bergdahl's family.

And that the family had examined the letters and saw things in both of them that only could have been written by Bowe. Things like a little paw print on the first one which used to be one of his traditional ways of signing off on letters and references to things that the family would talk about.

Now, they do start logically talking about things like "I'm being fed," "I'm OK", but the first one in particular devolves into the long sort of diatribe on God, faith, the weather, and it's really hard to follow. That is probably the best indication that we have that Bergdahl was under a tough situation when he wrote them. Maybe somebody was watching him. Maybe this was one of the only times that he got a moment out of his cell to write and he was taking advantage of that, to write as much as he could for as long as he could.

The Taliban sources I've spoken to have said that he was held in a cage after his second escape attempt, though he was also moved around. So sometimes it was a cage, sometimes it was a basement. He has told some of the people debriefing him that he had a hood over his head much of the time as well, except when he was eating or drinking.

So, yes, he probably wrote these letters but people were watching him and his state of mind can't have been good.

CUOMO: Wow. I mean, we had heard about one escape. Now, they're saying two attempted escape, kept in a cage, really harsh conditions.

How do you explain some is in cursive, some is in block letters. That may be an indication of monitoring.

DOZIER: It can be. If his captors were trying to read what he was writing and they often are able to read block print but not cursive. It's like, I'm OK in spoken Arabic, I can't read it. It's the kind of also indicates that maybe he's trying to send a message.

The second letter there does seem to be aware that there was an investigation into his departure from the base and he seems to be -- he is defending himself. He's telling his family, tell those doing the investigation in D.C. Wait until all the evidence comes in. He talks about the conditions being bad, not having confidence in his leadership, and the situation being very unsafe.

CUOMO: Does it sound -- what's the take? Is it like it's propaganda driven or do you think this comes across as specific insight?

And as Kim is answering, throw up the pictures we have of the letters so people can see for themselves the difference in writing and these different excerpts.

But, Kim, what's your answer to that question?

DOZIER: You know, it can be one of two things. He could be defending himself saying I walked off that base for a reason because the conditions weren't acceptable. But it was also good message that the Taliban would want out, that the morale was bad, that the soldiers on the ground didn't have the confidence of their leadership.

The investigation into Bergdahl's disappearance from the base did conclude that leadership at his platoon was lacking. Two of his leaders were replaced during the time he was there.

CUOMO: There's a lot of speculation about that to be sure. That will be part of any eventual investigation. The Pentagon, as you know, has been very strong on telling people to wait on making any type of conclusion about desertion versus walking off and doing something stupid.

Let's pull up one part of one of the letters where he's saying, "If this letter makes it to the USA, tell those involved in the investigation there are more sides to the situation." He adds, "Please tell D.C. to wait for evidence."

Two questions: one, why can't he spell? And, two, what do you think that suggests about his motivation when he walked off?

DOZIER: Well, he was home-schooled. And I also did get to read the letters from Bergdahl's family back to him. We haven't released those. They're private. They're about things like family births and things going on inside their home. But there are spelling mistakes in their letters as well.

CUOMO: OK.

DOZIER: So, this just seems to be part of Bowe's tradition.

CUOMO: OK.

DOZIER: "The Washington Post" also obtained some of his journal writings that he mailed off just before walking off base. And this script and this spelling is very similar to those.

CUOMO: Two things to finish on for now, Kim, really, thank you so much for doing this reporting. You've always been known for great work in this area and this certainly advances it. One, does this mean that the Red Cross knew where he was if they were able to get these letters? And, secondly, do you get the feel from the context and the writings that he left on purpose with a plan never to return or that he was just upset there? Can you answer those two?

DOZIER: You know, I am not sure what the Red Cross knew. They were rather upset that I had obtained these letters because one of the things that they do is send thousands of these messages on behalf of detainees every year. And they rely on confidentiality.

These letters were provided to me by people in contact with the Taliban. The Taliban decided to release them. And as to Bowe's state of mind, it does seem to point to him making a decision that he felt the conditions were too dangerous and he was deciding to leave them.

Now, you talk to defense officials or those who served with him, they say that's not good enough.

CUOMO: Not good enough meaning what?

DOZIER: That's not good enough, that's not a good enough reason, you don't walk off your base.

CUOMO: Oh, sure.

DOZIER: You don't disappear when you have orders that you think are unjust or you have a situation that you think is unfair. There's a chain of command. There's a way to complain about those things. But the one thing the Pentagon and Bowe Bergdahl do seem to agree on is that they both want to wait until they have time to hear from Bergdahl, hear his whole story before passing judgment.

CUOMO: It definitely takes us one step closer to whether or not -- because what's the ugliest speculation, oh, he wanted to be with the Taliban and all this that we learn about the escapes and the treatment paints a little bit of a different picture of these letters help as well.

Kim Dozier, thank you for doing what you do best, which is bringing those news from difficult. Thanks for being with us.

DOZIER: Thanks, Chris.

CUOMO: Brianna, over to you.

KEILAR: Thanks, Chris.

Next up on NEW DAY, Hillary Clinton blasts a radio host during an interview when the issue of gay marriage comes up. We'll bring you the fiery exchange and what she had to say about the accusation that she had a, quote, "change of heart for political reasons."

Plus, Chris Christie cuts a rug. There you have it, right? You can see the governor bust a move with Jimmy Fallon. It's really something you don't want to miss. We'll show you the whole thing.

(COMMERCIAL BREAK)

CUOMO: Welcome back.

There is a lot going on to start your NEW DAY. So, let's get right to John Berman. He's in for Mickey, and he has the top stories.

JOHN BERMAN, CNN ANCHOR: Thanks, Chris. Boy, is there a lot going on?

Starting in Iraq, the U.S. is weighing how to respond as radical Islamists take over key Iraqi cities and move closer to the capital. President Obama saying he will not rule anything out if it keeps militants from gaining any permanent foothold in Iraq and Syria. Air strikes are a possibility but White House spokesman Jay Carney says U.S. ground troops not an option.

Texas Republican Congressman Pete Sessions will not be the next house majority leader.